Functional diversity of tree cavities for secondary cavity-nesting birds in logged subtropical Piedmont forests of the Andes

Abstract

Studies about functional ecology have increased in the last years and they are currently an important element for the understanding of ecosystem processes. The aim of this study was to compare different functional traits of cavity trees for secondary cavity-nesting birds, between unlogged (control forest) and conventionally logged sites in subtropical piedmont forests of NW Argentina. Between 10 and 20 plots per site were established and were grouped according to the treatments (control forest and logged forest) for statistical analyses. We measured and defined the following cavity tree traits potentially important for cavity-nesting birds: diameter at breast height (DBH), cavity height, cavity entrance size and cavity internal depth. Besides, abundance and taxonomic richness of cavity tree species were calculated, as well as functional indices: Functional Richness (FRic, amount of functional niche volume filled by cavity tree species in the community), Functional Evenness (FEve, measures the regularity of the distribution of cavity tree species abundances and dissimilarities in functional space), Functional Divergence (FDiv, quantifies how cavity tree species diverge in their abundance-weighted, distances in functional space) and Community-Weighted Mean (CWM, mean of trait values present in the community weighted by the relative abundance of species bearing each value). The main results showed that logged sites (relative to control sites) had: (1) lower abundance and taxonomic richness of cavity trees; (2) lower functional richness; (3) higher functional evenness, which may be due to the uniformity in distribution of the traits of the cavity tree species in space; (4) lower ‘Community-Weighted Mean’ of cavity size, possibly due to the fact that larger cavities need larger tree species and they are the most extracted in logged sites. Understanding how the functional traits of cavity trees are affected may help decision makers to implement sustainable policies for conservation of secondary-cavity user birds, and consequently, of the ecological services they provide.